The present invention relates to an apparatus for measuring the air flow around a turning rotor. More specifically, the present invention measures the air flow exiting the cooling vents of a turning rotor.
Wheeled vehicles are typically slowed and stopped with a braking system that generates frictional forces. Many braking systems include a rotor attached to one or more of the vehicle wheels for rotation therewith, and a caliper assembly secured to a non-rotating component of the vehicle, such as the vehicle frame. The rotor includes an annular peripheral section having friction surfaces disposed on opposite sides. The caliper assembly includes a pair of brake pads disposed adjacent the rotor friction surfaces, and a moveable piston operatively connected to one or more of the brake pads. When the driver brakes the vehicle, hydraulic or pneumatic forces move the piston which clamps the pads against the friction surfaces of the rotating rotor. As the brake pads press against the moving rotor friction surfaces, frictional forces are created which oppose the rotation of the wheels and slow the vehicle. The friction converts the vehicle's kinetic energy into large quantities of heat, much of which is absorbed by the friction surfaces and conducted throughout the rotor.
It is important to dissipate the heat and cool the rotor. If the rotor is not adequately cooled, the heat generated during braking can build up in the rotor and reduce braking performance by creating longer stopping distances, shorten the life of the rotor, or even cause brake failure. The rotor also helps to keep the brake pads cool by absorbing the braking heat and moving it away from the pads. However, the rotor can only absorb a finite quantity of heat. An inadequately cooled rotor will approach its heat storage capacity and absorb less heat, causing the brake pads to overheat thus reducing braking performance and the life of the brake pads.
Rotors are commonly cooled using moving air which absorbs the heat from the rotor and carries it away. It is known to "ventilate" the rotors by forming holes or vents through the friction surfaces. As the rotor turns, air is moved through the vents. The moving air absorbs heat from the rotor friction surfaces and cools the rotor. Other ventilated rotors include outer friction surfaces formed on a pair of annular friction plates joined together by spacers or posts in a mutually parallel, spaced apart relationship to form spaces or vents therebetween. The vents are open at the radially inner and outer edges of the friction plates to form air passages between the friction plates. As the vented rotor turns, air forced through the vents between the friction surfaces absorbs heat from the friction plates and cools the rotor. Other portions of the rotor are also cooled as the air moves past them and through the vents. The cooling effectiveness of the vents is proportional to the quantity of air passing through the vents. The more air which moves through the vents and past the rotor surfaces, the more heat that is dissipated and the greater the cooling effects. Therefore, it is desirable to move as much air as possible through the vents.
The shape, spacing and orientation of the posts determine the amount of air which passes through the vents. When designing the vents to most effectively cool the rotor, the shape, spacing and orientation of the posts must be optimized to move the greatest amount of air. It is desirable to provide an air flow test apparatus for measuring the amount of air moving through the vents when the rotor is turning in order to quantify the cooling effectiveness of a particular vent design.